I'm making an explorers tea coat. it's two old leather coats, one black, one brown cut up and riveted together. It's got loads of stuff on it already, but the main thing I need is a "centrepiece" for the back of it - between the shoulder blades... and I've run out of ideas.

There will be 4 3/4" clear plastic tubes leading to it from 2 horizontal brass tubes, one above and one below. So I have the idea of it being some sort of pulsating or rotating circular "engine" that the tubes connect to...

light:Is a plasma ball too tacky ?Would a circular arrangement of nixie tubes look good - but are they too fragile ?

"steam"I looked at the steam generators for trains but they only last a few minutes and get very hot apparentlya USB powered water diffuser is embarrassingly patheticSome sort of smoke machine then, but is there a battery powered one anyone has used ?

Anything available with a spinning disc or fan or something that is battery powered and I could modify ? I'd prefer something I can take apart rather than build

Glass nixie tubes are, in my opinion, unsuitable for clothing.A plasma disc is more reasonable than a plasma ball merely for getting through doorways, sitting in chairs etc.You might add something made with LED badges.Look at the Halloween stuff, there may be something fun to repurpose. It's usually well worth a lookBetween Halloween and Christmas there are often a lot of decorations and costume pieces useful for steampunk projects.

Because of the location, I immediately thought of wings. You could rig them to flap with a simple motor. But that doesn't sound like where you're going.You could adapt a computer fan to battery power. And there are small battery motors available cheap.Or a clock movement, and substitute discs for hands.

What about a tiny infinity mirror. I used a Christmas rope light to make an 18 inch diameter one for my nephew a few years back and the continuous spiral of light made it look like an SF film worm hole. For one small enough to put on your back you could use el wire.You could make the leather around the "hole" look a little burnt and say you lost the ray gun fight.

(I have wanted to try this for a few years but it never goes with my outfits )

Its of options depending on what's available.A faux escutcheon plate in plastic with rub and buff.Add a H harness style setup for anything heavy.Maybe vasaline/uranium glass with a few black lights/LEDs set to light in sequence.